Acid-base-forming foods

The foods we eat are digested; they break down into either an acid or an alkaline end-product in our tissues.
This end-product is called the "ash" and is what remains in the body after the food has been broken down.

Foods that produce an alkaline ash are called "base-forming food" whereas those producing acid ash are called "acid-forming" foods.

The presence of some kinds of acid in food does not necessarily make it an acid forming food in the body. As an example, after digestion, citric acid (found in lemons) becomes volatile and is easily exhaled by the lungs and what is left behind in the body is an ash that is actually alkaline.